Antibodies have long been used in medical diagnosis, e.g., determining blood types, and in biologioal experimentation. With development of techniques of producing monoclonal antibodies which make it possible to obtain homogenous, highly specific antibodies, Kohler G. and Milstein, C.: (1975) Nature (London) 256 495-497, the utility of antibodies has been greatly increased. Unlike antibody fraction which were previously available and which were actually heterogeneous mixtures of a number of antibody molecules reactive with a variety of antigenic determinants, the molecules in a monoclonal antibody are all identical and generally are reactive with a single antigenic determinant or a group of closely related antigenic determinants. Monoclonal antibodies are therefore much more precise probes for detecting the presence of a particular substance than were previous heterogeneous antibody fractions. The precise selectivity of monoclonal antibodies makes them particularly useful for diagnostic purposes and even as therapeutic agents against selected biological material, such as tumor cells. Monoclonal antibodies have been used to detect and isolate biological substances which were were previously unknown.
Generally, monoclonal antibodies are produced by immunizing an animal with a biological specimen or other foreign substance, obtaining antibody-producing cells from the animal, and fusing the antibody-producing cells with strains of neoplastic cells, e.g., tumor cells, to produce hybridomas which are isolated and cultured as monoclones. The monoclonal hybridomas may either be cultured in vitro or may be grown in vivo as tumors in a host animal. Because each antibody-producing cell produces a single unique antibody, the monoclonal cultures of hybridomas each produce a homogenous antibody fraction which may be obtained either from the culture medium of hybridoma cultures grown in vitro or from the ascitic fluid, or serum of a tumor-bearing host animal.
Not all of the hybridoma clones which result from fusing neoplastic cells with antibody-producing cells are specific for the desired foreign substance or antigen because many of the hybridomas will make antibodies which the animal's immune system has generated in reaction to other foreign substances. Even monoclonal antibodies against the subject antigen will differ from clone to clone because antibodies produced by different clones may react with different antigenic determinants of the same molecule. From each clone, therefore, it is necessary to obtain the resulting antibody or the antibody-containing medium, serum or ascitic fluid and test its reactivity with the subject biological material and to test its specificity by determining what other biological material, if any, it recognizes. While the necessity of characterizing the antibody of each clone adds to the complexity of producing monoclonal antibodies, the wide variety of homogeneous antibodies which may be obtained gives investigators a number of very precise tools to map the structure and development of somatic cells.